1. Field of the Invention
This invention generally relates to I/O cells with programmable active input bias. More specifically, the invention relates to a circuit architecture, and to a method of using this circuit architecture, for an actively compensated and programmable impedance I/O.
2. Prior Art
CMOS I/O drivers require a tightly controlled driver impedance to maintain signal integrity when switched at high speeds. I/O drivers have been designed that maintain the driver's impedance by making adjustments for Integrated Circuit (IC) process variations, temperature and voltage changes. These I/O designs consist of a custom I/O circuit design and the overhead circuitry required to set the driver impedance for a given IC process; and then maintain this impedance when changes in temperature and voltage are sensed.
The design of such dynamically-controlled and programmable impedance drivers is often quite complex compared to I/O cell designs without this type of control. Custom circuit design, test, verification and characterization of the I/O can be quite time consuming and costly. For each additional technology offering, where these same controlled impedance I/O's are required, the lengthy design process must begin again.